The present invention pertains generally to printed circuit board layout, and more particularly to a novel method and apparatus related to printed circuit board contact pads.
Frequently, engineers may decide to make changes to the layout of a printed circuit board. These changes may be due to one of many reasons, including correcting errors, product improvements, revisions or improving the layout of a printed circuit board. There may be additional connections made to contact pads on the printed circuit board, rerouted connections, wrong connections removed and reconnected to the correct contact pad. Often, there are numerous engineering changes to a printed circuit board, including rerouting of numerous connections between pads on the printed circuit board. If the printed circuit board has already been manufactured, this may be very difficult and expensive to re-engineer the connections to the contact pads.
By way of example only, one area in which re-engineering of a printed circuit board happens frequently is in the printed circuit board (PCB) automatic tester environment. A simplified diagram of one such PCB tester is shown in FIG. 1. A target PCB 105, typically populated with electronic components 107, is held in a stable fashion by a target board support 130. A plurality of probes 135 make contact at one end with points of interest on the target PCB 105 to be tested. The other end of each probe 135 makes contact with electrical contact points on one side of a fixture PCB 110. On the opposite side of the fixture PCB 110 are another set of electrical contact points, each of which is associated with a pin 120. The pins 120 are utilized to connect various points of the fixture PCB 110, with a resource of tester 150 via testing interface 115, shown without detail in FIG. 1.
Thus, the fixture PCB 110 is employed as a way of mechanically customizing the testing interface 115 for any particular target PCB 105. Typically, significant forces are applied to one or both sides of the fixture PCB 110 by way of the probes 135 and the pins 120. To prevent inordinate flexing of the fixture PCB 110 under such forces, structural elements, such as spacers 140 and fixture adapter 111, are employed. These structural elements may predominantly reside on the upper or lower side, or both, of the fixture PCB 110.
Often, changes to the connections embodied in the fixture PCB 110 are required. These changes are necessitated by modifications in test strategy, causing a change in the number of points of interest to by checked on the PCB 105, a modification in how the points of interest are tested, a correction to the test methodology or a correction to the design of the PCB 105. Also, a design modification to the target PCB 105 may cause a change of location in the points of interest on the target PCB 105. As a result of these modifications or corrections, commensurate changes in the location or number of the probes 135, or in how the probes 135 are connected to the pins 120, may be required. In such cases, changes in the electrical connections implemented within the fixture PCB 110 are necessary.
FIG. 2A shows a blown-up, simplified fixture PCB 110 with under side interface pins 120A and 120B making contact with contact pads 125A and 125B, respectfully. Contact pads 125A and 125B are electrically connected to connection pads 127A and 127B via traces 123A and 123B. Connection pads 127A and 127B are electrically connected to connection pads 137A and 137B on the topside of the fixture PCB 110 via internal PCB trace 121A and 121B. Test probes 135A and 135B make electrical contact with contact pads 131A and 131B, which are electrically connected with connection pads 137A and 137B via trace 133A and 133B. If an engineering change order, design change, test change or other reason requires an electrical connection between the resource of contact pad 125A and the resource of contact pad 125B, an electrical connection is made via small-gauge wire-wrap wire 139, or other known connection means between connection pad 127A and connection pad 127B, as shown in FIG. 2B. It is difficult to make multiple contacts to a single contact pad. Engineering change order and other electrical connections are typically made between the connection pads 127A and 127B, as connecting wires or soldering directly to the contact pads 125A and 125B would degrade the electrical qualities of contact pad 125A and 125B.
Additional electrical connections can be made to connection pad 127A via small-gauge wire-wrap 141 and other resource connection pads on the PCB 110, as shown in FIG. 2C. On a large complex PCB, removing resources is difficult. Therefore, if engineering change orders or other design modifications later require the removal of a resource from the layout; the exposed electrical trace 123A is severed between the contact pad 125A and the connection pad 127A. This effectively removes the test resource interface pin 120A from the test probe 135A. Once a resource has been removed from the design layout, it is difficult to recover the resource.
Accordingly, there is a need for a simple method to reroute interconnect on a PCB, disconnect resources and reclaim disconnected resources on a PCB during multiple revisions and engineering change orders to the PCB.